The present invention relates to a method of cleaning by plasma etching. In particular, the present invention provides a method for cleaning reaction chambers employed in the deposition and etching of layers on silicon substrates utilizing plasma etching.
The cleaning of reaction chambers, given deposition and etching in the field of material coating, is acquiring increasing significance. For instance, the cleaning of reaction chambers is vital within the process sequence for manufacturing integrated circuits from silicon substrates. An increased need for highly efficient and production-compatible cleaning steps arises in conjunction with the increase of the chip integration density.
In addition to the wafer cleaning, the cleaning of the reaction chambers has proven especially critical. Every manufacturing cycle for producing layers or, respectively, for etching layers repeatedly utilize reaction chambers. With respect to silicon wafers, the cleaning of the reaction chambers is necessary no layer than following a specific throughput.
During the processes, the inner surfaces of these reaction chambers can become coated or contaminated at unwanted locations. In time, these parasitic layers lead to disturbances in the process management or to contamination of the workpiece to be coated or etched. In the present case, these layers are composed of organic polymers and/or oxides and nitrides of silicon. D. Widmann et al., "Technologie Hochintegrierter Schaltungen", Springer-Verlag 1988, illustrates the current state of deposition or etching technology, particularly sections 3.1.1, 5.2.3 and 5.3.5.
The disturbance of the processes or the contamination of the workpieces compels frequent chamber cleaning. This in turn leads to increased wear of parts, further including costs associated with replacement parts and preparation. In addition, increased frequency of chamber cleaning leads to high maintenance outlay in view of personnel and work time and, last but not least, to manufacture outages due to the low throughput and high down time. These disadvantages reach an especially great degree when the reaction chambers are opened and the layers and coats are conventionally cleaned by mechanical removal.
The known introduction of hydrogen fluoride vapor into the reaction chambers proves similarly disadvantageous in view of a great outlay in the work, operating and waste disposal reliability. Oxidic and nitridic layers are thereby converted into the vapor phase. However, the aggressivity of hydrogen fluoride jeopardizes the long-term stability of the partially surface-finished system parts.
Since reaction chambers are generally already designed for plasma-enhanced deposition of etching, current chamber cleaning ensues on the basis of in situ dry etching with etching gases activated in the plasma. Under current processes, layer-dissolving gases are introduced into the reaction chamber. A plasma generated with the existing electrodes then activates these gases. Then, the various fractions of the introduced gases react with the residues deposited in different thicknesses at the inner surfaces of the reaction chamber to form gaseous products that are conveyed out with vacuum pumps.
Fluoridated carbons, such as CF.sub.4 and C.sub.2 F.sub.6, or similar fluorine-containing gases, such as SF.sub.6 and NF.sub.3, are currently utilized in situ cleaning. The latter, however, again cause a deterioration of the surface quality of the inside chamber parts and therefore involve the disadvantages already cited above. On the other hand, a simultaneous polymer deposition accompanies etching with CF.sub.4 and C.sub.2 F.sub.6. This undesired polymer formation occurring during the course of cleaning is also indirectly negatively felt in that, among other things, the layers deposited in the next process step adhere poorly to the polymer layer. As a result, the easily detachable particles can often cause damage to the wafer.
Adding oxygen (O.sub.2) to the etching gas can in fact reduce the polymer formation. However, without opening the chamber and using mechanical cleaning, the cleaning effect usually remains unsatisfactory. Moreover, O.sub.2 plasma etching of organic residues is a relatively slow process that takes many times the actual coating or etching time to carry out and thus leads to disproportionately long cleaning times.